From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 43223C43381 for ; Sun, 17 Feb 2019 06:23:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1182E2196F for ; Sun, 17 Feb 2019 06:23:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ifcnmcwM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728294AbfBQGXk (ORCPT ); Sun, 17 Feb 2019 01:23:40 -0500 Received: from mail-pg1-f196.google.com ([209.85.215.196]:39281 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726057AbfBQGXk (ORCPT ); Sun, 17 Feb 2019 01:23:40 -0500 Received: by mail-pg1-f196.google.com with SMTP id r11so6857822pgp.6 for ; Sat, 16 Feb 2019 22:23:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=nm7Mpr2bFzDsTZtDgyvgfnqAVAhEse/hD66HPwpevYI=; b=ifcnmcwMlqknwcmblNlaOdEKIdi2A7JylegsmM4qPX6LKXhT0ZDMyL5XKSNZUgZ1ol mbTn8MatZvfW5RlESuur/dZZzaVRaepLswtWfvSL93RWTQhoKtUMHJWKOU/QNCNchpSq Lu/svA4tSsxsI85nS1x9uShfXffajFxM2Df+Mdl4vi3qRz8X6Aqpo0XR/+GbJkZzCj3o NrvzGzrRqu5fKqZmH5Bo49rKdOqKBSjfMxBPMNGzaNhsrFFesFV6le1PgjnnT6AA94Jy T015qKwtZu05dS2Hm8uFvn5dZTIBkwQrJe1YESNzYmnhfz/SujlmJTpbMmLCkpdxS5A1 LbgQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=nm7Mpr2bFzDsTZtDgyvgfnqAVAhEse/hD66HPwpevYI=; b=MDwwc1LwuGrYoXRCHFxCfURXAyf/KzfjbLkBgc4AH35fnZCj0dhsOPryGCJvbhlavq nVbgW1ZxNwsOEara7epEsTaytBJmMn4rhfEw8v+iJnoYk1/Yi3hBbP5xp8Nr9Km7FQvu Ze7T/m7PsUZeai/wJsqxi9tlLx1KZXaipX5M9HM91jI9f5Gy+79SYBcyJr0s9ms4SPbm rJQz3diDj1HK6Fkwrrfai9QSOMCCGZQvpABKVha7KUR+sFJmL5gXBidSdP4gtZTCHXYE Ti/23KhTIb66izVY2qITq4e0Bj+fUwuSp5kcsuZXjASsvhiP30C1WFMVHdr8ISWnyjEg jKZQ== X-Gm-Message-State: AHQUAuYxTMSTzEVKtGtkyoJBO/nCY7+jsJbhzZut4+O0lkv5zAAYVOf1 3zKl0qi0o8KDibsXb/nrFrZ348uz X-Google-Smtp-Source: AHgI3IbaL+qoncpcwlKwPaLrZSlwDbREXbJesWUb4jxQUmO9VmgguFlB3LYaCIFe0NomUSbpOkUzig== X-Received: by 2002:a62:b40b:: with SMTP id h11mr313568pfn.108.1550384618640; Sat, 16 Feb 2019 22:23:38 -0800 (PST) Received: from localhost (220-245-128-230.tpgi.com.au. [220.245.128.230]) by smtp.gmail.com with ESMTPSA id f13sm13736786pfa.132.2019.02.16.22.23.36 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 16 Feb 2019 22:23:37 -0800 (PST) Date: Sun, 17 Feb 2019 17:23:33 +1100 From: Balbir Singh To: Segher Boessenkool Cc: Michael Ellerman , erhard_f@mailbox.org, jack@suse.cz, linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, aneesh.kumar@linux.vnet.ibm.com Subject: Re: [PATCH] powerpc/64s: Fix possible corruption on big endian due to pgd/pud_present() Message-ID: <20190217062333.GC31125@350D> References: <20190214062339.7139-1-mpe@ellerman.id.au> <20190216105511.GA31125@350D> <20190216142206.GE14180@gate.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190216142206.GE14180@gate.crashing.org> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Feb 16, 2019 at 08:22:12AM -0600, Segher Boessenkool wrote: > Hi all, > > On Sat, Feb 16, 2019 at 09:55:11PM +1100, Balbir Singh wrote: > > On Thu, Feb 14, 2019 at 05:23:39PM +1100, Michael Ellerman wrote: > > > In v4.20 we changed our pgd/pud_present() to check for _PAGE_PRESENT > > > rather than just checking that the value is non-zero, e.g.: > > > > > > static inline int pgd_present(pgd_t pgd) > > > { > > > - return !pgd_none(pgd); > > > + return (pgd_raw(pgd) & cpu_to_be64(_PAGE_PRESENT)); > > > } > > > > > > Unfortunately this is broken on big endian, as the result of the > > > bitwise && is truncated to int, which is always zero because > > (Bitwise "&" of course). > > > Not sure why that should happen, why is the result an int? What > > causes the casting of pgd_t & be64 to be truncated to an int. > > Yes, it's not obvious as written... It's simply that the return type of > pgd_present is int. So it is truncated _after_ the bitwise and. > Thanks, I am surprised the compiler does not complain about the truncation of bits. I wonder if we are missing -Wconversion Balbir